Mike Everman wrote:another misconception we need to dispell is that there is compression that leads to combustion. Combustion begins on or around zero compression in these motors. The heat release needs to begin as the pressure is rising.

Thank you, Mike. Combustion may even begin before the chamber is back to atmospheric. It might be argued that at least in some designs (and the Reynst comes to mind) perhaps combustion never really stops. What the Kadenacy pressure peak at the end of the intake part of the cycle does is intensify combustion that is already taking place.

These pressure ideas made me think it would be fun to try a pulsejet at a higher altitude, say something like the base of Mt. Hood or near Santa Fe or something. And jam jars too. And then on the opposite end of the spectrum it would fun to have a pressure chamber and see how the increased ambient air pressure affects the design of a pulsejet, if you could shorten the length more or would you want to lengthen it?
I guess it might be possible to put a pressure head on the front end of a pulsejet if the valves sealed perfectly and leave the tail at the ordinary STP of the air around us. It would be interesting to see how all the curves on the chart go, some unexpectedly I'm sure.
I wonder how hard it would be to pull a partial vacuum by using a pipe to suck air from the tail region of a pulsejet to simulate forward flight in a Lockwood?
Mark

Mark
Changing the working preasure of the pulse jet is the direction that I want to go, except instead of decreasing the preasure like at high altitude I want to see what will happen if you increase the preasure at the intake and the tail pipe at the same time, kind of like putting the pulse jet in a new enviroment where the air is a lot more dense. The cycle should increase in frequency. For example maybe I could make a rotor tip mounted engine and have a ram difuser that the whole pulse jet fits into so you get preasure at both ends. What do you guys think?

Larry posted a handful of scoops and diffuser for that not too long ago. It's a great idea. I'm still on the fence about whether the increased energy is worth the drag. I have no numbers to substantiate that opinion, though. I have seen it mentioned, but I haven't seen any experiments done.

SNECMA was big into pulse combustors in turbojets, a similar problem, getting high ambient at both ends.

I was rereading the Lockwood literature, the 80 mph drive with the Lockwood improved thrust he said, perhaps because of less recirculation of hot gases. I suppose this means it got more fresh air, which in turn caused it run/combust better.
He also states that the workings of the augmenter is not fully understood, but I wonder too if the augmenter might also be doing the same, that is, causing the exhaust gases to be evened out, thrown back/ejecting spent products farther away from the engine instead of "balling" as the ejected gases interact with the outside air , so that there is less recirculation of hot gases/spent air as well?
And thus if the pulsejet is moving at a high rate of speed, the augmenter is a hindrance not only for drag but also for redundancy of getting good evacuation.
This topic is about midway down this page.
Markhttp://www.blastwavejet.com/pulsejet.htm

Greg O'Bryant wrote:I want to see what will happen if you increase the preasure at the intake and the tail pipe at the same time, kind of like putting the pulse jet in a new enviroment where the air is a lot more dense.

So do I. That is exactly what my Constant Flow concept should do.

Mike Everman wrote:Larry posted a handful of scoops and diffuser for that not too long ago. It's a great idea. I'm still on the fence about whether the increased energy is worth the drag.

Mike, in real terms, thereâ€™s no such thing as drag until you mount the engine on a vehicle. Remember the WW II-era big radials? One look at those engines and everyone in his right mind would say that such draggy engines would never make it in the air. Yet, Vought Corsair was one of the fastest of them all, and Focke Wulf 190 was no slouch either. Itâ€™s what the airframe builders did with those engines that counted.

Say, I want to fly myself. My butt has a cross section you can hide a General Electric fanjet behind. So, I have to have a broad fuselage anyway. Tucking in an engine behind me is a no-brainer. Flying a model plane is different, of course, but other factors (mass etc.) will always dictate that the models be flown powered by relatively simple engines.

Turning the moving gas around , a la Lockwood, actually transfers twice the momentum of the gas to the engine. Its probably the major source of thrust.

Re: the Tesla vavle,
try thinking of it as laminar flow one way, highly turbulent the other.
As it stops the exiting gas, it will reduce its speed to zero (or something),
implying it should impart the momentum of the gas to the engine.

The problem I sould see then is that you have an intake valve that is full of exhaust gas instead of fresh air, and that exhaust gas has to be sucked into the engine first. Thus it would always be running on exhaust gas (which I'm told in turbines is about 30% oxygen depleted. They run them lean to avoid the high temperatures that burn out pulse-jets. Pulsejet exhaust is therefore probably more than 50% depleted)
So, a valve on the inlet would have to have a small volume.

How about putting a gun silencer on it?
They absorb much of the gas momentum, then vent it at a much lower velocity.

"A long time ago, I proposed a cylindrical form of the Tesla valve, Which you get if you rotate the original item around one of the long sides. You get a tube with a serrated center spike and a series of conical washers, Which would be very easy to manufacture cheaply and just stack in a tube. Also It would add another brake to the outgoing gas by making it expand and contract Alternatively. stages 2-3 I think would be just enough for it to work quite Effectively. "

No one has made a serious try at the Tesla valve in a pulsejet that I know of, so no one knows for sure it won't work. It sure has been pitched on the forum several times, so I suggest a thorough search for the term and the threads that discuss it.

My research, opinion and experience and those smarter than me call it a dead end though, and my prediction is it won't be good even if you can get a pulsejet using it to resonate, which I doubt. It will just manifest itself as a horrible leak on exhaust, a poor, long slow intake full of exhaust products, when you want the quickest, shortest path for clean intake air that makes acoustic sense. The tesla would have no acoustic property that we spend so much effort to get right.

The acoustic properties of the intake dictate all. No kidding. Even a valve type has the same acoustic requirement; even in the same proportions as a valveless. That is not obvious, and a lot of people think the two types of motor are very different, but they are not.. For instance, a valve type won't run if the valve is leaky (which changes the acoustics of half of the cycle), and it wont run if it has no inlet bell. For best performance, that intake bell has a very specific acoustic length. If you do not know the difference between acoustic and physical length, you should do as I did and spend some time on the hyperphysics site, and it's discussion on open and closed pipe acoustics.

I've seen people do and have done things with pulsejets that people were lining up to say are not doable, so it's possible someone will prove me wrong! Ten years of building, analyzing and testing point to simplicity and short, smooth paths for gas to get in and out in a hurry for the best performance. Flow shenanigans are fun to think about, of course, but these things are very finicky about too much surface area for the volume.

There are an infinite number of shapes that will support self sustaining pulsating combustion, and a very finite number that will give a compelling thrust to volume ratio, and a truly tiny number that have low TSFC (thrust specific fuel consumption). A pulsejet with a Tesla valve may get a resonance going, but I'll bet real money it will never impress us with thrust.

I agree with Mark Everman. Trick non-return intakes are a waste of energy. Whatever energy goes into the trick intake is lost to no good use. In effect, you are spending energy to defeat the energy you have just produced. Makes little sense. Far better to use the intake to produce thrust when it's not sucking fresh air in. Non-return intakes are dinosaurs.

Yes, that one was reportedly tested by Messerschmitt successfully, but why would you need one? What's wrong with the simple bending of the tube backwards? It's not like youl need fantastic aerodynamic qualities in real life. You are not building a cruise missile, right?

Bruno Ogorelec wrote:Yes, that one was reportedly tested by Messerschmitt successfully, but why would you need one? What's wrong with the simple bending of the tube backwards? It's not like youl need fantastic aerodynamic qualities in real life. You are not building a cruise missile, right?

No, but it's nice to have the option.
Seriously though, the straight-line compactness is an advantage in mounting it and I must confess to preferrring the look as well. Also, it becomes possible to use it as the core of a ramjet.

How does the Messer compare to the Lockwood interms of fuel use, power-weight ratio, and efficiency?